I wasn't 100% happy with the product but I believe that it was my fault as I wanted a long sleeve top with was containing lycra and I didnt investigate the product in more detail.
Line Spacing: Line spacing is important as word spacing. Normally when text is designed for t-shirts, it will have too much space between the lines. This will look odd on a printed t-shirt. Therefore, make sure that the line space is adjusted accurately on the design.
Line Breaking: You can have the text in any format. However, when the text is designed for the t-shirt, it should be readable and clear. Therefore, it is important to work on the line breaking to make sure the text is readable.